I’d like to add a left hand thumb hole to one of my whistles to see if I like it. But this is something I wouldn’t want to try at home. Are there any whistle makers or repair persons out there who will do this modification? Has anyone on the forum had this done?
I love thumb holes, added them to quite a few whistles, and my new whistles are designed with this seventh hole.
Adding the thumb hole to a whistle is not such a big deal. Half way between hole 1 and 2 and 180 degrees around is a good location, then start with a smaller hole and gradually increase the hole size till the tuning is comfortable.
Usually a thumb hole added later will create a slightly sharper C# (or equivalent) note (because of the added venting when all fingers, including thumb, are lifted), but this is usually not a problem, or quite good, as the C# tends to be a bit flat, in order to help the cross-fingered Cnat.
Where are you located?
I am sure any whistle maker/tweaker here can help you.
Cheers,
Hans
Why not have a go on a cheap whistle first (I’m assuming that you don’t want to do it at home because your whistles are expensive?). It might be worth trying your own hole tweak before paying someone to do it on a more expensive whistle.
I second trying it on a cheapo first to see what alterations might happen to that one. Adding tone hole/s after the instrument is made might change the overall feel of your whistle enough that if you really like it as it is, you may not afterwards. Seen it happen and twas really sad…
Brigitte
I live in the Washington, D.C. (USA) area. There are a number of good woodwind techs around here that should be able to add the thumb hole. Maybe I can find one with some experience with penny whistles. Also, I sent an email to Kelischek (most of my whistles are Susatos) inquiring about this modification. Hopefully I’ll hear back from them soon. And I see that the maker Michael Burke offers the thumb hole as an option on his whistles. Possibly I’ll look into purchasing one of his whistles. But I’d rather have the hole added to my Susatos as I now own several and like the way they play. If it seems like there will be a wait involved getting the work done by a pro I might give it a go myself. I think though I’d probably make a hash of it as I’m not too handy with tools. Probably drill a hole in my finger.
Which, of course, would allow you to vent the hole without lifting the finger. 
What note would this thumb be making? I never play my Feadog D and could see myself using it for such experimentation.
C natural on a D whistle
first finger down, all others & thumb up
Okay, that makes sense.
And placing a similar hole between F# and E would make an Fnat hole, yes?
The purpose of the thumb hole is to get C nat. without cross fingering. See Michael Burke’s site where he explains the advantages of the thumb hole. And I heard back from Kelischek and they are emphatically against adding the thumb hole. Something about compromising the “integrity” of the whistles. They seem to have a very different philosophy than Burke.
Well, I went ahead and drilled a thumb hole in my Susato C whistle (which I don’t use much), though I didn’t manage to center it 180 degrees from the top holes. It’s a little off to the side (I figured I’d make a hash of it but at least I didn’t drill a hole in my finger). So far I’m liking it pretty well. It definitely makes certain fingerings alot easier though there are some note sequences where the oxxooo C fingering would be better. Also it gives a very good 2nd octave C nat. Much better than the combination cross fingering and half hole I was using for the high C. I think I’ll work with it for a while before I try it on my other whistles.
Good man. Well done! 
Now, go ahead and drill an Fnat hole and let me know how it goes. Having someone else do the experiment first is much better!
yup!
DON’T! This is much trickier to place in a useful position for the right hand thumb, and even if you get it right it may be really awkward to use, it is for me, as the right thumb is much more important to hold the whistle.
It is much easier to half-cover the fifth hole for a Fnat, and since it is the biggest hole anyway, it ususally gives a decent Fnat.
Big fan of thumb holes, both on whistles and flutes.
It took me awhile to get used to playing with them.
I’ve had flutesmyth’s do this for me, both on whistles and flutes.
My Susato C whistle has one; Chris Abell has done it
for free for his whistles.
I took my D and Bb whistles over to a friends’ house who’s a master carpenter with a full arsenal of drills, bits, clamps, vises, etc. and we got the thumb holes put in pretty well. The idea is to after making sure of the positioning of the hole start the drilling using a very small drill bit, checking the pitch with a tuner, and gradually increasing the size of the hole until the pitch comes up to (A) 440. I think we went up 3 or 4 increments to find the right pitch. At that point the thumb hole was still a good bit smaller than the smallest top hole which is good as that makes it easy to seal. After getting in some playing I’m finding quite a few situations where the thumb hole really slicks up the action. It makes some passages and phrases so easy it feels like cheating. It won’t completely replace the cross fingered C but it’s a valuable alternate fingering. Amost like having a side C on the saxophone. Sometimes you just got to have it.
I finally made the time today to try this on an old Walton’s I forgot I had. Just drilled, filed and smoothed the hole, and tuning is dead-on.
Wow, I really like it. 
It gives a loud, clear C natural, and feels very intuitive. As suggested, I wouldn’t use it exclusively, but I expect I’ll use it a lot, especially where that note is prominent or sustained.
Very, very nice! 
Then lengthen the foot of the tube and put in a C hole for your bottom pinkie and you’ve got a brass recorder in C!
Adding a low C to the whistle may or may not be a good idea (I don’t think I’d want a low C) but it wouldn’t make it a recorder. If I were to add anything to the whistle beyond a left hand thumb hole it would be double holes on 5 and 6. Yeah, I know. Heresy. But I like to play jazz and blues on the whistle in addition to ITM and I need the full chromatic scale. But I’m starting to get fairly adept at half-holing so double holes might be a solution to a non-existant problem.